My woodworking shop has a CNC router so lots of used router bits. I was wondering if I could sharpen them to work as end mills. Unfortunately most of them are compression spirals or down spirals. Less than ideal for metal. I found a 1/2" carbide, Marathon coated two flute down spiral and decided to sharpen the end only to give it a try. I used my Shars single point tool grinder and a diamond wheel. I'm far from an expert at setting it up but managed to get the chipped end of the bit to clean up. Put it on the Jet mill and a chunk of aluminum in the vice. First tries were running at 500rpm and moderate freed rate. It cut but not ideal. By increments, I increased both the rpm and feed rate until I got to 4,000rpm. WD40 and a faster feed than I normally use. .200" DOC. Chips flew all over but the resulting surface was reasonably good. I added it to my end mills that I had sharpened yesterday. Once the tool grinder is set up, I can sharpen end mills at a pretty fast clip, ends only. 2, 3, or 4 flute but no more flutes than that. HSS or carbide with the proper wheel. Lathe tools are easy to sharpen.